Indexable insert

ABSTRACT

The indexable insert possesses two parallel cutting edges on opposite sides of an indexable insert body in the form of a rectangular block. In the intermediately placed top surface descending toward the center line (M) there is a chipbreaking structure comprising alternating projections and recesses. These projections and recesses constitute a row, centered on the center line (M), of spherical-like chipbreaking bodies, between which concave chip guiding surfaces are formed. During metalcutting operations, this provides an even flow of chips with the formation of short chips which are free of grooves and tears along the edges.

BACKGROUND OF THE INVENTION

The invention relates to an indexable insert having two parallel cuttingedges formed on opposite sides of an indexable insert body at the samelevel, between which a top surface is provided with a chipbreakingstructure formed by projections and recesses.

Indexable inserts exist in various different basic forms and in numerouscustomized designs, which by dint of their geometry and composition areadapted for different purposes and materials to be machined.

SUMMARY OF THE INVENTION

The invention makes available an indexable insert which is amenable touse in high performance applications while at the same time producingshort, smooth and readily controlled chips at a lower power requirement.

In the indexable insert in accordance with the invention, the mutuallyalternating projections and recesses of the chipbreaking structuredefine a continuous undulating line, the crests of such undulating linerising above the cutting edges and the troughs being below the cuttingedges; in a section athwart the center line the top surface hasextending inward from each cutting edge part, a descending top surfacepart, which rises toward the center line and merges with thechipbreaking structure. Preferably, the chipbreaking structure isdefined by a row of at least generally part-spherical chipbreakingbodies, said row being parallel to the cutting edges and being centeredabout the center line with concave chip guiding faces being formedbetween the said bodies.

Further advantageous developments and convenient forms of the inventionwill be understood from the following detailed descriptive disclosure inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic perspective representation of the indexableinsert, whose top surface is indicated by intersecting grid lines.

FIG. 2 is a plan view of the indexable insert.

FIG. 3 is a sectional view taken on the line III in FIG. 2.

FIG. 4 is a partially sectioned side elevation of one cutting edge ofthe indexable insert.

DETAILED DESCRIPTION OF THE INVENTION

The indexable insert illustrated in FIG. 1 comprises an indexable insertbody 10 of a generally rectangular block having a flat base surface,four side surfaces extending perpendicularly to such base surface and atop surface, which possesses inwardly descending top surface parts and achipbreaking structure arranged along the center line M of the indexableinsert body 10. Two cutting edges 12 and 14 are formed at the same leveland are parallel to one another between the top surface and the twolonger side surfaces.

The chipbreaking structure comprises generally part-sphericalprojections 16 in a row centered on the center line M of the coversurface, such projections alternating with concave recesses. As seen ina section along the center line M, the projection 16 and the recesses18, and as apparent from FIG. 4, define a continuous undulating line,whose crests rise above the cutting edges 12 and 14 and whose troughsare lower than such cutting edges 12 and 14. As seen in a sectionathwart such center line M, the top surface respectively has, extendinginward from a cutting edge part in the direction of the center line M, adescending top surface part 20, which, rising again toward the centerline M, merges with the projections 16 and the recesses 18.

In the case of the preferred embodiment, which is depicted in FIGS. 3and 4 with the main geometrical characteristics, the clearance angle atthe side surface 10a is 0°. At the cutting edge 12 there is a risingcutting edge land 22, which has a negative rake angle α of approximately15°. The cutting edge land 22 is radiused to merge with a flat part ofthe descending top surface part 20. This radiused zone has a radius R₁of less than 1 mm, as for instance, 0.8 mm. The width b of the cuttingedge land 22 is less than 1 mm and amounts to, for example, 0.6 mm. Theflat part of the descending top surface 20 possesses a positive rakeangle β of approximately 14°.

In FIG. 3 the section is taken through the lowest point T of one of therecesses 18. The descending top surface part 20 merges with a slightcurvature, which has a radius R₂ of, for example 10 mm, with the lowestpoint T thereof. Following this, there is an ascent with a somewhatsmaller radius R₃ of curvature of, for instance, 8 mm, which merges witha convex part of the recess 18, whose radius R₄ of curvature is lessand, for example, amounts to 5.5 mm.

Considered again in a direction athwart the center line M but throughone of the projections 16, there is a form which in principle issimilar, but at a greater height. The descending top surface part 20merges here with a flat intermediate part 24, which is adjoined, in aninward direction toward the center line M, by a concavely rising partwith a radius R₅, which may be the same as the radius R₅ and, forexample, amounts to 8 mm. This concavely ascending part finally runsinto a convex apical part, whose radius R₆ of curvature is somewhat lessthan the radius R₄ of curvature and, for instance, amounts to 6 mm.

As related to the lowest point T, the flat intermediate part 24 of thetop surface is approximately half way up in relation to the common planeof the cutting edges 12 and 14. The apical point S of the projection 16extends by an amount h past the level of the cutting edges 12 and 14;this amount t is equal to approximately 1/3 (33%) of the amount 5, bywhich the lowest point T is lower than the height of the cutting edges12 and 14. This amount t is equal to, for example, 1.5 mm so that h isequal to approximately 0.5 mm. Furthermore, the reader will see fromFIG. 3 that the crest of the convex part of the recesses 18 is generallyat the crest of the convex part of the recesses 18 is generally at thesame level as the flat intermediate part 24.

The undulating line indicated in FIG. 4, which is defined by theprojections 16 and the recesses 18 along the center line M, consists ofalternating convex circular arc sections with a radius R₇ of, forinstance, 5.5 mm and concave circular arc sections with a somewhatsmaller radius R₈ of approximately 5 mm.

Furthermore, FIG. 4 will be seen to indicate one of several threadedholes 26, which extend perpendicularly through the base surface of theindexable insert body 10 and serve for attachment of the indexableinsert on a cutting tool.

The indexable insert is manufactured from conventional sintered carbidematerial. It is suitable for use in high performance applications. Theprojections 16 act as chipbreaking bodies, which in conjunction with therecesses 18 placed in between, serve to ensure the production of short,smooth chips without furrows and marginal tears. All in all, the flow ofchips may be readily controlled. The chipbreaking structure does notinvolve providing additional drive power and, owing to the even flow ofchips, the indexable insert has a long working life.

What is claimed is:
 1. An indexable insert having two parallel cuttingedges (12, 14) formed on opposite sides of an indexable insert body atthe same level, between which a top surface is provided with achipbreaking structure formed by projections and recesses, wherein in asection along a center line (M) parallel to the cutting edges, mutuallyalternating projections (16) and recesses (18) define a continuousundulating line (M) which has crests (S) rising above the cutting edges(12, 14) and troughs falling below the cutting edges (12, 14) and in asection athwart center line (M) has a top surface with descending topsurface parts (20) extending inward from each cutting edge which mergewith the chipbreaking structure.
 2. The indexable insert as claimed inclaim 1, wherein as seen in a section athwart the center line (M) andthrough the crest (S) of a projection (16), the descending top surfacepart (20) extends inwardly from the cutting edges (12, 14) andintersects with a flat intermediate part (24) remaining generally at thesame level, wherein the intermediate part (24) merges with an arcuatelyrising initial part of a projection (16).
 3. The indexable insert asclaimed in claim 2, wherein each arcuately rising part is made up of aconcave circular arc section and an inwardly adjoining convex circulararc section.
 4. The indexable insert as claimed in claim 3, wherein theconcave circular arc section possesses a substantially larger radius(R₅) than the convex circular arc section (R₆).
 5. The indexable insertas claimed in claim 1, wherein as considered athwart the center line (M)and generally in the middle between two adjacent projections (16), thedescending top surface part (20) merges into an arcuate trough whichdescends to a lowest point (T) and then ascends again.
 6. The indexableinsert as claimed in claim 5, wherein each arcuate trough comprises aconcave circular arc section and an inwardly adjoining convex circulararc section.
 7. The indexable insert as claimed in claim 6, wherein theconcave circular arc section possesses a substantially larger radius(R₂) than the convex circular arc section (R₄).
 8. The indexable insertas claimed in claim 1, wherein between each cutting edge (12, 14) andthe descending top surface part (20) an ascending cutting edge land (22)is formed.
 9. The indexable insert as claimed in claim 1, wherein thecontinuous undulating line is composed of alternating convex and concavecircular arc sections.
 10. The indexable insert as claimed in claim 9,wherein the radius (R₇) of the convex circular arc sections isapproximately 10% larger than that radius (R₈) of the concave circulararc sections.
 11. The indexable insert as claimed in claim 1, wherein acutting edge land (22) extends inwardly from the cutting edges (12, 14)and has a negative rake angle (α) of approximately 15°.
 12. Theindexable insert as claimed in claim 1, wherein a cutting edge land (22)extends inwardly from the cutting edges (12, 14) and merges with the topsurface part with a radiused zone.
 13. The indexable insert as claimedin claim 12, wherein the radiused zone has a circular arc with a radius(R₁) of approximately 0.8 mm.
 14. The indexable insert as claimed inclaim 1, wherein the descending top surface part (20) has a positiverake angle (β) of approximately 14°.
 15. The indexable insert as claimedin claim 2, wherein the lowest point (T) of the descending top surfacepart (20) is at a distance approximately twice as far below the level ofthe cutting edge (12, 14) as the flat intermediate part (24).
 16. Theindexable insert as claimed in claim 15, wherein the flat intermediatepart (24) connects the descending top surface part (20) with theprojection (16) and wherein the crest of the troughs extend toapproximately the level of the flat intermediate part (24).
 17. Theindexable insert as claimed in claim 5, wherein the crests of theundulating projections extend above the cutting edges (12, 14) byapproximately 33% of the depth (t) from the lowest point (T) of the topsurface to the level of the cutting edge (12, 14).
 18. The indexableinsert as claimed in claim 1, wherein the chipbreaking structurepossesses a row of at least generally part-spherical chipbreakingbodies, said row being arranged parallel to the cutting edges andcentered on the center line (M), between which bodies concave chipguiding surfaces are formed.